Understanding Compound Paths

Illustrator lets you carve holes inside a path. You can then see through these holes to objects and colors that lie behind the path. A path with holes in it is called a compound path.
If you convert a letter such as B or O into outlines, the letter is automatically converted into a compound path.
To make a compound path, do the following:

Draw two shapes.
Make one smaller than the other. You can use any tool to draw either shape, and the paths can be open or closed.

Select both shapes and choose Object>Compound Paths>Make.
Where the two shapes overlap, the compound path is transparent. Where the shapes don't overlap, the path is filled.

Edit the individual shapes in the compound path with the direct selection tool.
After you combine two or more shapes into a compound path, select the entire path by clicking on it with the arrow tool. If you want to select a point or segment belonging to one of the subpaths -- that's the official name for the shapes inside a compound path -- press Command-Shift-A (Mac) or Control-Shift-A (Windows) to deselect the path, and click an element with the direct selection tool. You can then manipulate points, segments, and control handles as usual.

At this point you might ask, "Why do you need a path with a hole in it? Why not just stick the smaller path in front of the bigger path and fill in the smaller path with the background color?" Two reasons:

First, the background may contain lots of different colors. The "B" on the left is a proper compound path, allowing us to see through the holes to anything behind it.

Second, working with opaque paths limits your flexibility. Even if you can get away with filling an interior path with a flat color, you'll have to change that color any time you change the background or move the objects against a new background. But with a compound path, you can move the object against any background without changing a thing. You can even add effects like drop shadows without modifying the compound path one iota. It's flexibility at its finest.

Now, as we said, Illustrator automatically turns letters into compound paths. But you may want to create additional compound paths of your own. Doughnuts, ladders, eyeglasses, windows, and ski masks are just a few of the many items that lend themselves to compound paths.

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